Seat track assemblies are commonly used for forward and rearward comfort adjustment of seats, particularly seats affixed to motor vehicles. Such seats normally have a seat base and a seat back, with the seat back pivotably connected to the seat base by recliners. It is desirable for such seats, especially those positioned in the front row of a motor vehicle, to have upper seat tracks which are slidable over lower seat tracks, where the tracks are releasably secured together by a latch assembly at a position selected by an operator. To enhance stability, typically two pair of tracks are used, each pair positioned generally near one side of the seat base.
Known latch assemblies include a latch member pivotably mounted on the upper track and provided with a series of windows. The windows engage teeth which are typically either cut out of the lower track or positioned on a plate attached to the lower track. Other designs place the latch teeth on the latch and place the windows on a part which is engaged by the latch. A lever is normally attached to a handle or towel bar. Actuation of the towel bar urges the latch windows out of engagement with the teeth, permitting comfort adjustment by allowing the upper track to slide with respect to the lower track. Release of the towel bar allows the latch to resecure the seat tracks together.
Such known designs for securing upper tracks to lower tracks can have several problems. Seat track positioning is ordinarily not "infinite". That is, the incremental amount of adjustment is restricted by the spacing and size of the teeth. Further, due to tolerance stack ups and other minor errors in design tracks on one side of the seat may be slightly misaligned with tracks on the other side of the seat so that the latch windows engage the teeth on one side but do not completely engage the latch teeth on the other side. In addition, when the seat track assembly is subjected to vibrational loading, as in a motor vehicle, the teeth may vibrate against the windows, producing undesirable noise.
One design showing an infinitely adjustable seat track mechanism is shown in U.S. Pat. No. 5,481,941 to Premji. Premji relies on a spring loaded pawl block extending from the lower track to releasably bias a striated roller towards one downward flange of an upper track, and thereby releasably secure the upper track with respect to the lower track. However, this design is complex, as the block requires a framework to slide in, is relatively expensive to manufacture, and is somewhat bulky, taking up valuable space below the seat base.
In view of the foregoing, it is an object of the present invention to provide a seat track assembly having both reduced cost and enhanced manufacturability. It is another, related object of the present invention to provide such a seat track assembly with infinite adjustment and reduced chucking and rattling problems. It is a further object of the present invention to provide a seat track assembly that is highly reliable in operation.